Scintillator evaluation method

Abstract

A scintillator evaluation method according to the present invention includes steps S1 to S5. In step S2, a waveform f(t) of an electric signal output from a photodetector that has received scintillation light generated by a scintillator is obtained. In step S3, computation is performed to deconvolve the electric signal waveform f(t) with an impulse response function i(t) of the photodetector. In step S4, the result of the computation in step S3 is fitted with a model function represented by the convolution of s(t) and p(t), where s(t) is a time response function of the scintillator, including information concerning both rising and falling the generation of scintillation light due to interactions with radiation, and p(t) is a function representing the single photon time resolution of the photodetector. In step S5, the time response of the scintillator is evaluated on the basis of the result of the fitting. Thus, a scintillator evaluation method that makes it possible to evaluate the time response of a scintillator in short time with high accuracy is realized.

Description

Scintillator evaluation method

[0001] The present disclosure relates to a method for evaluating the temporal response of a scintillator.

[0002] Scintillators generate scintillation light upon interaction with high-energy radiation (e.g., gamma rays, X-rays, alpha rays, etc.) and may also generate Cerenkov light in addition to scintillation light. Scintillators are used in conjunction with photodetectors that receive the scintillation light (and Cerenkov light).

[0003] The photodetector used in the above configuration is, for example, a photomultiplier tube (PMT) and a silicon photomultiplier (SiPM), etc. PMTs and SiPMs are capable of photon counting measurements and are also capable of analog measurements.

[0004] SiPMs (digital SiPMs) capable of photon counting measurements can acquire information on all detected scintillation photons, and can therefore detect the time at which radiation interacts with the scintillator with a time resolution that is increased to the theoretical limit.

[0005] The digital SiPM can obtain information on Cherenkov photons, which are believed to be the first to be generated when radiation interacts with a scintillator. Furthermore, by adding the output signals from the digital SiPM, it is possible to evaluate the characteristics of the scintillator and evaluate the single photon time resolution (SPTR) of the SiPM with high accuracy.

[0006] On the other hand, compared to digital SiPMs, SiPMs capable of analog measurement (analog SiPMs) are still in use because they have higher photon detection efficiency, are easier to manufacture, easier to process output signals, and are easier to handle.

[0007] Radiation detectors including scintillators and photodetectors can be used in a variety of devices that detect radiation, as well as radiation tomography devices such as Positron Emission Tomography (PET) devices and Single Photon Emission Computed Tomography (SPECT) devices.

[0008] Scintillators made from various materials are known, and scintillators made from new materials are also being developed. One of the important evaluation items for scintillators is the time response of scintillation light generation due to interaction with radiation. Known methods for evaluating the time response of scintillators include the time-correlated single photon counting (TCSPC) method and the averaging method (Non-Patent Documents 1 and 2).

[0009] In the TCSPC method, when one of a pair of gamma-ray photons generated by an RI source traveling in opposite directions is incident on a scintillator to be evaluated, the scintillation light generated in the scintillator is detected by a photodetector, causing the photodetector to output a signal pulse, and the other photon is detected by a reference radiation detector, causing the radiation detector to output a synchronization pulse. The time difference between the signal pulse and the synchronization pulse is determined for each of the many photon pairs generated by the RI source, and the time response of the scintillator to be evaluated is evaluated based on a histogram of these time differences.

[0010] In the averaging method, when gamma-ray photons generated by an RI source are incident on a scintillator to be evaluated, the scintillation light generated in the scintillator is detected by a photodetector, and the waveform of the electrical signal output from the photodetector is obtained. The signal waveforms obtained for each of the many photons generated by the RI source are averaged, and the time response of the scintillator to be evaluated is evaluated based on the averaged waveform.

[0011] S. Qian, Q. Wu, L. Ma, Y. Zhu, et al., "LYSO scintillation light test with an ultra-fast MCP-PMT", J. Phys.: Conf. Ser., 2374, 012115 (2022)I. Gerasymov, S. Witkiewicz-Lukaszek, T. Zorenko, et al., "Effects of co-doping with divalent cations on performance of YAG:Ce,C scintillator", IEEE Trans. Nucl. Sci, Vol.70, pp.1362-1369 (2023)S. Gundacker et al., "Experimental time resolution limits of modern SiPMs and TOF-PET detectors exploring different scintillators and Cherenkov emission", Phys. Med. Biol., 65, 025001 (2020)Eric Berg, Emilie Roncali, Will Hutchcroft, Jinyi Qi, Simon R. Cherry, "Improving Depth, Energy and Timing Estimation in PET Detectors with Deconvolution and Maximum Likelihood Pulse Shape Discrimination", IEEE Trans. Med. Imaging, Vol.35, pp.2436-2446 (2016)M. V. Nemallapudi et al., "Single photon time resolution of state of the art SiPMs", JINST 11 P10016 (2016)

[0012] Although the TCSPC method can evaluate the time response of the scintillator with high accuracy, it takes a long time (e.g., 10 days or more to about one month) to obtain a histogram of the time difference between the signal pulse and the synchronization pulse. On the other hand, the averaging method can obtain an average waveform for a large number of photons incident on the scintillator in a relatively short time (e.g., 30 minutes or less), but the evaluation accuracy is low because the information includes the time response of the photodetector.

[0013] An object of the present invention is to provide a scintillator evaluation method that can evaluate the time response of a scintillator with high accuracy in a short time.

[0014] An embodiment of the present invention is a scintillator evaluation method, which is a method for evaluating the time response of a scintillator that generates scintillation light by interacting with radiation, and includes: (1) a signal waveform acquisition step of acquiring the waveform of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator, (2) a deconvolution calculation step of deconvolving an impulse response function of the photodetector with the waveform of the electrical signal, (3) a fitting step of fitting a calculation result from the deconvolution calculation step with a model function that indicates a probability density distribution of scintillation light components expressed by convolution of a time response function of the scintillator that includes information on both the rise and fall of scintillation light generated by interaction with radiation and a function that indicates the single-photon time resolution of the photodetector, and (4) an evaluation step of evaluating the time response of the scintillator based on the fitting result from the fitting step.

[0015] According to the embodiment of the present invention, the time response of a scintillator can be evaluated with high accuracy in a short time.

[0016] FIG. 1 is a diagram showing a measurement system for acquiring the impulse response function i(t) of a photodetector. FIG. 2 is a diagram showing a measurement system for acquiring the waveform f(t) of an electrical signal output from a photodetector that receives scintillation light generated by a scintillator to be evaluated. FIG. 3 is a diagram showing an example of the waveform f(t) of the electrical signal output from the photodetector. FIG. 4 is a diagram showing an example of the time response function s(t) of a scintillator. FIG. 5 is a diagram showing an example of a function p(t) representing the single-photon time resolution of a photodetector. FIG. 6 is a diagram showing an example of the impulse response function i(t) of a photodetector. FIG. 7 is a diagram showing an example of the results of a deconvolution operation of i(t) with respect to f(t). FIG. 8 is a flowchart of a scintillator evaluation method according to this embodiment. FIG. 9 is a diagram showing the results obtained by evaluating the time response of a BGO in an example. FIG. 10 is a diagram showing an enlarged portion of FIG. 9. FIG. 11 is a diagram showing the results obtained by evaluating the time response of a BGO in an example, in comparison with the evaluation results obtained using the TCSPC method. Fig. 12 is a diagram showing the results obtained by evaluating the time response of a BGO in an example, compared with the evaluation results described in Non-Patent Document 3. Fig. 13 is a diagram showing the results obtained by evaluating the time response of an LYSO in an example, compared with the evaluation results obtained by the TCSPC method.

[0017] Hereinafter, embodiments of the scintillator evaluation method will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0018] The scintillator evaluation method of this embodiment evaluates the time response of a scintillator based on the waveform f(t) of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator to be evaluated, and the impulse response function i(t) of the photodetector. t is a variable indicating time. Therefore, an example of a measurement system for acquiring i(t) and f(t) will first be described.

[0019] Fig. 1 is a diagram showing a measurement system for acquiring the impulse response function i(t) of a photodetector. The photodetector 12 outputs an electrical signal in response to the incidence of a photon v. The electrical signal output from the photodetector 12 is input to an oscilloscope 40, which acquires the waveform of the electrical signal. The photodetector 12 is, for example, a PMT or a SiPM. As shown in Fig. 2, the photodetector 12 constitutes a radiation detector 10 together with a scintillator 11 to be evaluated.

[0020] 1, the impulse response function i(t) of the photodetector 12 is obtained as follows: The voltage applied to the photodetector 12 is set as high as possible (for example, to +8.0 V, which is an overvoltage above the breakdown voltage) so that a single photon can be visualized using the oscilloscope 40 without an amplifier.

[0021] The range is set (for example, 1 mV / div) so that the entire waveform of a single photon falls within the voltage range of the oscilloscope 40. The trigger threshold of the oscilloscope 40 is set to 0.5 photons. Then, waveform acquisition is repeated until statistical noise becomes insignificant, and the waveform is averaged to obtain the impulse response function i(t) of the photodetector 12.

[0022] 2 is a diagram showing a measurement system for acquiring the waveform f(t) of an electrical signal output from a photodetector that receives scintillation light generated by a scintillator to be evaluated. The scintillator 11 to be evaluated and the photodetector 12 constitute a radiation detector 10. The scintillator 21 and the photodetector 22 constitute a radiation detector 20. The photodetector 22 is, for example, a PMT or a SiPM.

[0023] The radiation detector 10 and the radiation detector 20 are arranged opposite to each other. An arbitrary RI radiation source (for example, 22 A pair of gamma ray photons γ with energy of 511 KeV, which are generated by annihilation of an electron and a positron in the RI source, travel in opposite directions and are counted by the radiation detectors 10 and 20 simultaneously.

[0024] When one gamma ray photon γ is incident on the scintillator 11 of the radiation detector 10, scintillation light is generated in the scintillator 11. The scintillation light is received by the photodetector 12, and an electrical signal is output from the photodetector 12. The electrical signal output from the photodetector 12 is input to the oscilloscope 40 as a signal whose waveform f(t) is to be acquired.

[0025] When the other gamma ray photon γ is incident on the scintillator 21 of the radiation detector 20, scintillation light is generated in the scintillator 21. The scintillation light is received by the photodetector 22, and an electrical signal is output from the photodetector 22. The electrical signal output from the photodetector 22 is input to the oscilloscope 40 as a signal indicating the timing of coincidence counting of the photon pair.

[0026] The electrical signal output from the photodetector 22 is also input to a CFD (Constant Fraction Discriminator) circuit 30. An energy discrimination signal indicating whether or not the photon incident on the scintillator 21 of the radiation detector 20 is a gamma ray photon with energy of 511 KeV is output from the CFD circuit 30, and this energy discrimination signal is also input to the oscilloscope 40.

[0027] In the oscilloscope 40, when the energy discrimination signal indicates that the photon incident on the scintillator 21 of the radiation detector 20 is a gamma ray photon with an energy of 511 KeV, the waveform f(t) of the electrical signal output from the photodetector 12 is acquired using the time indicated by the timing signal output from the photodetector 22 as the reference time.

[0028] In the measurement system shown in Figure 2, to obtain the waveform f(t) of the electrical signal output from the photodetector 12, for example, the following is done: Reduce the light intensity to an extent that the saturation effect of the photodetector 12 is not visible, or reduce the voltage applied to the photodetector 12 to reduce the detection efficiency. Scale i(t) according to the applied voltage. Reduce the applied voltage to an extent that the crosstalk probability of the photodetector 12 can be sufficiently ignored.

[0029] When the oscilloscope 40 is operated in coincidence mode, the timing signal output from the photodetector 22 is delayed relative to the signal from the photodetector 12 so that the trigger time of the photodetector 12 does not depend on the rise time. The voltage range of the oscilloscope 40 is increased so that the entire waveform of the electrical signal output from the photodetector 12 can be seen.

[0030] In a radiation detector 10 including a scintillator 11 and a photodetector 12 to be evaluated, the time response function of the scintillator 11 is defined as s(t), a function representing the single-photon time resolution of the photodetector 12 is defined as p(t), and the impulse response function of the photodetector 12 is defined as i(t). The waveform f(t) of the electrical signal output from the photodetector 12 is expressed by the convolution of s(t), p(t), and i(t), as shown in the following equation (1):

[0031] Figure 3 shows an example of the waveform f(t) of the electrical signal output from the photodetector. Since f(t) is expressed as a convolution of s(t), p(t), and i(t), it is difficult to obtain information about s(t), p(t), and i(t) from f(t) alone. f(t) can be obtained using the measurement system described using Figure 2.

[0032] FIG. 4 is a diagram showing an example of the time response function s(t) of a scintillator. s(t) includes information on both the rise time r and the fall time d of the scintillation light generated by interaction with radiation. The rise time r and the fall time d differ depending on the scintillator material. The rise time r is often 1 ns or less. The fall time d is the time required for the scintillation light generated by interaction with radiation. 12 ) is about 300 ns, and LYSO (Lu 2-x Y x In the case of SiO5, it is about 30 to 40 ns. s(t) can generally be expressed as a weighted sum of multiple basic equations (the following equation (2)). t ０ is the time when the radiation interacts with the scintillator.

[0033] Figure 5 shows an example of a function p(t) that represents the single-photon time resolution of a photodetector. p(t) can be approximately expressed as a Gaussian function. The single-photon time resolution (SPTR) is given by the full width at half maximum of this function. The SPTR is approximately 100 to 300 ps, ​​which is short compared to the response of s(t).

[0034] FIG. 6 shows an example of the impulse response function i(t) of a photodetector. i(t) can be expressed as the sum of two types of exponential functions. i(t) can be obtained using the measurement system described with reference to FIG. 1. i(t) is a function specific to the photodetector, does not change with each radiation interaction event in the scintillator, and can be easily measured. Compared to SiPM, PMTs have larger current fluctuations in i(t).

[0035] When i(t) is deconvolved with f(t), the convolution of s(t) and p(t) is obtained as shown in the following equation (3). The convolution of s(t) and p(t) is expressed by the model function shown in the following equation (4). This model function indicates the probability density distribution of the scintillation light component generated in the scintillator and detected by the photodetector. σ in this equation corresponds to the SPTR of the photodetector. ρ ｉ is a weighting coefficient when s(t) is expressed as a weighted sum of multiple basic equations (the above equation (2)). A is a coefficient.

[0036] Furthermore, when the light generated by the scintillator contains a Cherenkov light component in addition to the scintillation light component, the result obtained by deconvolving i(t) with f(t) can be expressed by the model function F(t) shown in the following equation (5). This model function F(t) is the probability density distribution F of the scintillation light component generated by the scintillator. ｓ (t) and the probability density distribution F of the Cherenkov light component generated by the scintillator. ｃ It is expressed as the sum of (t) and .

[0037] Probability density distribution F of scintillation light component ｓ(t) is expressed by the following equation (6): The probability density distribution F of the Cherenkov light component ｃ (t) is expressed by the following equation (7) (see Non-Patent Document 5). erfc in equation (7) is the complementary error function expressed by the following equation (8). ρ ３ is a coefficient indicating the proportion of the Cherenkov light component. λ is a parameter that represents the interaction depth fluctuation of the photodetector. μ is a parameter that represents the expected value of the emission time of Cherenkov light. Δ is a parameter that represents the time fluctuation of the photodetector.

[0038] 7 is a diagram showing an example of the result of deconvolution of i(t) with respect to f(t). The result of deconvolution based on f(t) and i(t) obtained by measurement is expressed by the model function of the above formula (4). Therefore, by fitting the result of this deconvolution with the model function of the above formula (4), each parameter (ρ ｉ , r ｉ , d ｉ , σ) can be calculated.

[0039] 8 is a flowchart of the scintillator evaluation method of this embodiment. The scintillator evaluation method of this embodiment is a method for evaluating the time response of a scintillator that generates scintillation light by interacting with radiation, and includes an impulse response function acquisition step S1, a signal waveform acquisition step S2, a deconvolution calculation step S3, a fitting step S4, and an evaluation step S5.

[0040] In the impulse response function acquisition step S1, the impulse response function i(t) of the photodetector is acquired. Note that if the impulse response function i(t) of the photodetector is known, the impulse response function acquisition step S1 does not need to be performed. In the signal waveform acquisition step S2, the waveform f(t) of the electrical signal output from the photodetector that receives scintillation light generated by the scintillator is acquired.

[0041] In the deconvolution step S3, the impulse response function i(t) of the photodetector is deconvoluted with the electrical signal waveform f(t). This results in the convolution of s(t) and p(t). In the fitting step S4, the calculation result of the deconvolution step S3 is fitted with the model function of the above equation (4).

[0042] In the evaluation step S5, the time response (rising r, falling d) of the scintillator is evaluated based on the fitting result in the fitting step S4. The SPTR (σ) of the photodetector can also be evaluated.

[0043] In the signal waveform acquisition step S2, the electrical signal waveform f(t) may be acquired multiple times (e.g., several hundred to 1,000 times). In this case, in the deconvolution calculation step S3, an impulse response function i(t) is deconvolved for each of the multiple electrical signal waveforms f(t). In addition, in the fitting step S4, fitting is performed on the sum or average of the results of the deconvolution calculation for each of the multiple electrical signal waveforms f(t) in the deconvolution calculation step S3 (hereinafter referred to as "Evaluation Flow 1").

[0044] Alternatively, in the deconvolution calculation step S3, the impulse response function i(t) is deconvolved with the sum or average of the multiple electrical signal waveforms f(t) (hereinafter referred to as "evaluation flow 2"). By doing so, the time response of the scintillator can be evaluated with higher accuracy.

[0045] Next, the advantages of the scintillator evaluation method of this embodiment compared to conventional methods will be described. In the TCSPC method, the time difference between the signal pulse and the synchronization pulse is determined for each of a large number of photon pairs generated by an RI source, and the time response of the scintillator to be evaluated is evaluated based on a histogram of these time differences, so the evaluation takes a long time.

[0046] In contrast, the scintillator evaluation method of this embodiment evaluates the time response of a scintillator based on the waveform of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator to be evaluated. In this respect, the scintillator evaluation method of this embodiment is similar to the averaging method, and can evaluate the time response of a scintillator in a short period of time.

[0047] Both the scintillator evaluation method and the averaging method of this embodiment evaluate the time response of a scintillator based on the waveform of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator being evaluated. However, the averaging method does not take into account the contribution of the impulse response function i(t) of the photodetector or the function p(t) representing the single-photon time resolution of the photodetector in the waveform f(t) of the electrical signal output from the photodetector. Furthermore, the averaging method takes into account the trailing edge d but not the rising edge r in the time response function s(t) of the scintillator. Therefore, the accuracy of the trailing edge d obtained by the averaging method is poor.

[0048] In contrast, in the scintillator evaluation method of this embodiment, a fitting process is performed assuming that the waveform f(t) of the electrical signal output from the photodetector is represented by the model function of equation (4) above, so that the time response (rising edge r, falling edge d) of the scintillator can be evaluated with high accuracy.

[0049] In the method described in Non-Patent Document 4, the impulse response function i(t) of the photodetector is taken into consideration, but the function p(t) representing the single-photon time resolution of the photodetector is not taken into consideration. Also, in the time response function s(t) of the scintillator, the falling edge d is taken into consideration, but the rising edge r is not taken into consideration. Therefore, the accuracy of the method described in Non-Patent Document 4 is poor.

[0050] Next, an example will be described. In this example, in the measurement system shown in FIG. 2, a scintillator 11 to be evaluated was a scintillator having a size of 3×3×15 mm. ３ BGO or size 3 x 3 x 10 mm ３ LYSO was used.

[0051] A SiPM (S13360-3050 manufactured by Hamamatsu Photonics K.K.) was used as the photodetector 12 for detecting scintillation light generated in the scintillator 11 to be evaluated. ３ LYSO was used, and SiPM (S13360-3075 manufactured by Hamamatsu Photonics K.K.) was used as the photodetector 22. The time response of the scintillator to be evaluated was evaluated by evaluation flow 2 (number of times the electrical signal waveform f(t) was acquired in signal waveform acquisition step S2 = 1000).

[0052] 9 and 10 are diagrams showing the results obtained by evaluating the time response of the BGO in the example. Fig. 10 shows an enlarged view of the area enclosed by the dashed rectangle in Fig. 9. Figs. 9 and 10 show the results of the deconvolution of i(t) with f(t) and the fitting results using the model function (the above-mentioned equation (5)).

[0053] 10 also shows the probability density distributions of the Cherenkov light component and the scintillation light component in the fitting results, which were obtained by fitting the results of the deconvolution of i(t) with f(t) using the model function F(t) in equation (5).

[0054] The results obtained in this example are as follows: For the time response of BGO, the fall time d １ = 339 ns, d ２ = 24.7 ns, and the rise time r １ =r ２ The SPTR of the SiPM was 0.498 ns. The ratio of the Cherenkov light component to the scintillation light component of the light incident on the SiPM (ρ ３ / (ρ １ +ρ ２ )) was 0.53%.

[0055] 11 is a graph showing the results of evaluating the time response of the BGO in the example, compared with the results of evaluation using the TCSPC method, showing the fitting results of fitting step S4 in the example and the distribution of the time difference between the signal pulse and the synchronization pulse obtained for each of a large number of photon pairs using the TCSPC method.

[0056] As shown in this figure, the scintillator evaluation method of this example can accurately reproduce the evaluation results obtained by the TCSPC method. Furthermore, the time required for the evaluation of BGO by this example was 15.9 minutes, which was significantly shorter than the 27.4 days required for evaluation by the TCSPC method.

[0057] 12 is a diagram showing the results obtained by evaluating the time response of BGO in the example, in comparison with the evaluation results described in Non-Patent Document 3. In this diagram, the evaluation results described in Non-Patent Document 3 are shown in a histogram, and the fitting results obtained by fitting step S4 in the example are shown superimposed on this by a solid line.

[0058] Non-Patent Document 3 describes that when radiation interacts with a scintillator, the photon that is most likely to be Cherenkov light when detected by a photodetector is the first photon detected by the photodetector. As shown in this figure, the scintillator evaluation results of this example agree well with the evaluation results described in Non-Patent Document 3, and the peak enclosed by the dashed ellipse in the figure is thought to indicate Cherenkov light detection.

[0059] 13 shows the results of evaluating the time response of the LYSO in the example, compared with the results of evaluation by the TCSPC method, showing the fitting results of the fitting step S4 in the example and the distribution of the time difference between the signal pulse and the synchronization pulse for each of a large number of photon pairs obtained by the TCSPC method.

[0060] As shown in this figure, the scintillator evaluation method of this example can accurately reproduce the evaluation results obtained by the TCSPC method, even for a relatively fast scintillator such as LYSO. Furthermore, the time required for evaluation of LYSO by this example was 14.7 minutes, which was significantly shorter than the 9.7 days required for evaluation by the TCSPC method.

[0061] The scintillator evaluation method is not limited to the above-described embodiment and configuration example, and various modifications are possible.

[0062] A scintillator evaluation method of a first aspect according to the above embodiment is a method for evaluating the time response of a scintillator that generates scintillation light by interacting with radiation, and includes: (1) a signal waveform acquisition step of acquiring the waveform of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator; (2) a deconvolution calculation step of deconvolving the waveform of the electrical signal with an impulse response function of the photodetector; (3) a fitting step of fitting a calculation result from the deconvolution calculation step with a model function that indicates a probability density distribution of scintillation light components expressed by a convolution of a time response function of the scintillator that includes information on both the rise and fall of scintillation light generated by interaction with radiation and a function that indicates the single-photon time resolution of the photodetector; and (4) an evaluation step of evaluating the time response of the scintillator based on the fitting result from the fitting step.

[0063] In the scintillator evaluation method of the second aspect, in the configuration of the first aspect, the signal waveform acquisition step may be configured to acquire the waveform of the electrical signal multiple times, the deconvolution calculation step may be configured to perform a deconvolution calculation on each of the waveforms of the multiple electrical signals, and the fitting step may be configured to perform fitting on the sum or average of the results of the deconvolution calculation on each of the waveforms of the multiple electrical signals in the deconvolution calculation step.

[0064] In the scintillator evaluation method of the third aspect, in the configuration of the first aspect, the signal waveform acquisition step may be configured to acquire the waveform of the electrical signal multiple times, and the deconvolution calculation step may be configured to perform a deconvolution calculation on the sum or average of the waveforms of the multiple electrical signals.

[0065] In the scintillator evaluation method of the fourth aspect, in the configuration of any one of the first to third aspects, the fitting step may be configured to fit the calculation result of the deconvolution calculation step with a model function expressed as the sum of the probability density distribution of the scintillation light component and the probability density distribution of the Cherenkov light component.

[0066] In the scintillator evaluation method of the fifth aspect, in the configuration of any one of the first to fourth aspects, a photomultiplier tube may be used as the photodetector in the signal waveform acquisition step.

[0067] In the scintillator evaluation method of the sixth aspect, in the configuration of any one of the first to fourth aspects, a silicon photomultiplier may be used as the photodetector in the signal waveform acquisition step.

[0068] INDUSTRIAL APPLICABILITY The present invention can be used as a scintillator evaluation method that can evaluate the time response of a scintillator with high accuracy in a short time.

[0069] 10...radiation detector, 11...scintillator, 12...photodetector, 20...radiation detector, 21...scintillator, 22...photodetector, 30...CFD circuit, 40...oscilloscope

Claims

1. A method for evaluating the time response of a scintillator that generates scintillation light by interacting with radiation, comprising: a signal waveform acquisition step of acquiring the waveform of an electrical signal output from a photodetector that receives scintillation light generated by the scintillator; a deconvolution calculation step of deconvoluting the waveform of the electrical signal with an impulse response function of the photodetector; a fitting step of fitting a result of the deconvolution calculation step with a model function that indicates a probability density distribution of scintillation light components expressed by a convolution of a time response function of the scintillator that includes information on both the rising and falling edges of scintillation light generated by interaction with radiation and a function that indicates the single-photon time resolution of the photodetector; and an evaluation step of evaluating the time response of the scintillator based on the fitting result of the fitting step.

2. The scintillator evaluation method of claim 1, wherein in the signal waveform acquisition step, the waveform of the electrical signal is acquired multiple times; in the deconvolution calculation step, a deconvolution calculation is performed on each of the waveforms of the multiple electrical signals; and in the fitting step, fitting is performed on a sum or average of results of the deconvolution calculation performed on each of the waveforms of the multiple electrical signals in the deconvolution calculation step.

3. The scintillator evaluation method according to claim 1, wherein in the signal waveform acquisition step, the waveform of the electrical signal is acquired a plurality of times, and in the deconvolution calculation step, a deconvolution calculation is performed on a sum or an average of the waveforms of the plurality of electrical signals.

4. A scintillator evaluation method according to any one of claims 1 to 3, wherein in the fitting step, the calculation result from the deconvolution calculation step is fitted with a model function represented by the sum of a probability density distribution of a scintillation light component and a probability density distribution of a Cherenkov light component.

5. A scintillator evaluation method according to any one of claims 1 to 4, wherein a photomultiplier tube is used as the photodetector in the signal waveform acquisition step.

6. A scintillator evaluation method according to any one of claims 1 to 4, wherein in the signal waveform acquisition step, a silicon photomultiplier is used as the photodetector.

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